The present invention relates to a disc drive slider having an adjustable fly height, and more particularly to a disc drive slider having a piezoelectric shear based transducer for magnetic spacing control of the read/write head fly height.
Disc drives are well known in the art and comprise several discs, each disc having several concentric data tracks for storing data. A read/write head is used to read from or write to a data track on a disc. The head is positioned above a data track on a disc by moving an actuator suspension arm on which the head is attached. The head is carried in a slider which flies a small distance above the disc due to an air bearing created as the disc is spun. A pre-load in the suspension arm maintains the downward force on the slider. The distance at which the head is suspended above the disc is called the fly height. To meet the demand for increased areal density on discs, the head must fly at ever decreasing distances from the disc surface.
Several variables affect the fly height of the slider and thus the distance between the head it carries and the disc surface. For instance, fly height is impacted by such factors as the curvature or roughness of the disc surface, shock and vibration, and variation in the aerodynamics of the slider due to changing the orientation and position of the slider. Particularly, it is a challenge to keep the head at the required fly height as the head is moved back and fourth by the actuator arm to position it above different tracks. Vibrations in the system caused by the spindle motors also effect fly height.
In an attempt to control the fly height, design changes to the suspension on which the head is attached have been implemented. In addition, the shape of the slider has been altered in an attempt to affect the aerodynamics involved. Other attempts involve placing transducers on the head suspension mechanism in an attempt to change the pre load on the air bearing, or bending the slider via piezoelectric elements. Often these remedies are very expensive to manufacture, and do not address all of the variables affecting fly height, including the slider orientation relative to the disc due to changes in air bearing shape.
One attempt to control the fly height of the slider is disclosed in U.S. Pat. No. 4,853,810 entitled xe2x80x9cMethod and Apparatus for Controlling the Fly Height of the Head in Magnetic Storing Unit.xe2x80x9d Yet another method of controlling fly height is disclosed in U.S. Pat. No. 5,021,906 entitled xe2x80x9cProgrammable Air Bearing Slider including Magnetic Read/Write Element.xe2x80x9d
Thus, there is a continuing need in the art for a slider having an adjustable fly height that is feasible to manufacture and can be easily controlled to move the read/write head in relation to the disc surface.
The present invention makes it possible to vary the fly height of a portion of a slider carrying a read/write head to insure a more accurate and reduced distance between the read/write head and the surface of the disc. To achieve this, a shear transducer is incorporated into the slider which allows a portion of the slider carrying the read/write head to be adjusted. The shear transducer comprises a layer of piezoelectric material added to the slider so that a portion of the slider carrying the read/write head can be moved when the shear transducer is energized. To cause the transducer to shear, a voltage is applied across the piezoelectric layer. The piezoelectric layer is polarized so that when a voltage is applied, the portion of the slider carrying the head can be moved closer to or further away from the disc surface in a vertical direction relative to the disc.
To control the movement of the transducer, a closed-loop control system is used. The control system includes a sensor for measuring the spacing between the head and the disc surface, an estimator to determine the voltage and an estimated position of the read/write head based on the sensor data, and a feedback controller for adjusting the voltage applied to the shear transducer based a comparison of the sensed position and a desired fly height. Once a voltage is applied to the shear transducer, the fly height of the slider portion carrying the head is measured, and the voltage is adjusted based on this measurement so that the piezoelectric layer either raises or lowers the portion of the slider carrying the read/write head.